Multi-elevational antenna systems and methods of use

ABSTRACT

The present disclosure provides systems and methods associated with an antenna system comprising a tension member configured to be towed by an aerial platform and/or secured to an orbiting satellite. In some embodiments, a first end of the tension member may be secured to the aerial platform and the second end may extend unsecured from the aerial platform at a different elevation than the first end. A plurality of antenna assemblies, each comprising at least one antenna, may be secured to and spaced along the length of the tension member. Each of the plurality of antennas may be adapted for use with a particular frequency or frequency bandwidth. For example, each of the plurality of antennas may be adapted or tuned for one or more frequencies useful for synthetic aperture radar (SAR). In some embodiments, a receiving system, a communication link, and/or an antenna location system may be utilized.

If an Application Data Sheet (ADS) has been filed on the filing date ofthis application, it is incorporated by reference herein. Anyapplications claimed on the ADS for priority under 35 U.S.C. §§119, 120,121, or 365(c), and any and all parent, grandparent, great-grandparent,etc. applications of such applications, are also incorporated byreference, including any priority claims made in those applications andany material incorporated by reference, to the extent such subjectmatter is not inconsistent herewith.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and/or claims the benefit of theearliest available effective filing date(s) from the following listedapplication(s) (the “Priority Applications”), if any, listed below(e.g., claims earliest available priority dates for other thanprovisional patent applications or claims benefits under 35 USC §119(e)for provisional patent applications, for any and all parent,grandparent, great-grandparent, etc. applications of the PriorityApplication(s)). In addition, the present application is related to the“Related Applications,” if any, listed below.

PRIORITY APPLICATIONS

None

RELATED APPLICATIONS

U.S. patent application Ser. No. 13/915,418, titled MULTI-ELEVATIONALANTENNA SYSTEMS AND METHODS OF USE, naming William D. Duncan, RoderickA. Hyde, Jordin T. Kare, and Lowell L. Wood as inventors, and filed Jun.11, 2013, is related to the present application.

U.S. patent application Ser. No. 13/915,425, entitled MULTI-ELEVATIONALANTENNA SYSTEMS AND METHODS OF USE, naming William D. Duncan, RoderickA. Hyde, Jordin T. Kare, and Lowell L. Wood as inventors, and filed Jun.11, 2013, is related to the present application.

If the listings of applications provided above are inconsistent with thelistings provided via an ADS, it is the intent of the Applicant to claimpriority to each application that appears in the Priority Applicationssection of the ADS and to each application that appears in the PriorityApplications section of this application.

All subject matter of the Priority Applications and the RelatedApplications and of any and all parent, grandparent, great-grandparent,etc. applications of the Priority Applications and the RelatedApplications, including any priority claims, is incorporated herein byreference to the extent such subject matter is not inconsistentherewith.

TECHNICAL FIELD

This disclosure relates to aerial antenna systems. More specifically,this disclosure relates to systems and methods for securing a pluralityof antennas at differing elevations to an aerial platform. Specificapplications of the antenna systems as they pertain to syntheticaperture radar are also provided.

SUMMARY

The present disclosure provides various systems and methods useful forradio communications, radiolocation, and/or radar techniques. Forexample, an antenna system as described herein may be used in syntheticaperture radar (SAR) systems for combining SAR data into an image.Spaceborne and/or airborne synthetic aperture radar (SAR) systems mayutilize various techniques for combining SAR data into an image. In someembodiments, multiple-pass SAR imaging utilizes SAR images acquired onmotion paths separated in elevation and/or direction. The SAR imagesfrom the varying elevations and/or directions are then synthesized toimprove elevational resolving power. Accordingly, three-dimensional (3D)imaging and/or mapping may be performed using data obtained from anantenna on an aerial platform moved over a target surface at multipleelevations. This may be useful for terrain mapping, analysis, objectdetection, and/or classification of objects.

In some embodiments, an antenna system may be towed by an aerialplatform or secured to an orbiting satellite. The antenna system mayinclude a tension member, such as a cable, having a first end and asecond end. The first end may be secured to the aerial platform and thesecond end may extend unsecured from the aerial platform at a differentelevation than the first end. A plurality of antenna assemblies may besecured to and spaced along the length of the tension member. Eachantenna assembly may include one or more antennas. Each of the antennasmay be adapted for use with a particular frequency, frequency band,frequency range, and/or frequency bandwidth. For example, each of theantennas may be adapted or tuned for one or more frequencies useful forSAR or other radio or radar technique(s). Since the second end of thetension member is unsecured to the aerial platform and extends at adifferent elevation than the first end, each of the antennas may belocated at a different elevation while the aerial platform is in motion.The tension member may be, for example, between 2 and 2000 wavelengthsof an antenna's tuned frequency. Longer tensions members may be usefulin some applications, such as high frequency systems. Shorter tensionmembers, such as those using antennas spaced by less than a quarterwavelength, may also be utilized.

The antenna system may receive and/or transmit electromagnetic energyusing the plurality of antennas secured to the tension member at variouselevations. In some embodiments, signals may be coupled to and/or fromthe antenna locations via a signal carrier. For example, an opticalfiber may function as a signal carrier to convey data between areceiving system and an attached antenna. In various embodiments, powermay be supplied to active devices attached to the tension member, suchas active electronic circuits associated with the antenna assemblies.The power may be supplied without affecting the performancecharacteristics of the antennas.

In some embodiments, a receiving system may be communicatively connectedto each of the plurality of antennas via one or more communicationlinks. For example, an optical cable extending adjacent to, entwinedwith, or integrated with the tension member may communicatively connecteach of the plurality of antennas or antenna assemblies to a receivingsystem. The receiving system may be a data storage system configured tostore information associated with received electromagnetic energy. Inother embodiments, the receiving system may re-transmit (e.g., forsubsequent storage or processing) the electromagnetic energy received bythe antennas. The plurality of antennas may be communicatively connectedto a receiving system (e.g., a storage system, a processing system, are-transmission system, etc.) via a wireless connection, an opticalfiber, an electrical conductor, and/or other communication technique ormedium.

In various embodiments, precise knowledge and/or control of the spatialpositions and/or orientations of the antennas relative to each other orto the aerial platform may be utilized, for example, to enable coherentprocessing of SAR signals. Various devices and systems may be used todetermine the positions of the antennas. In some embodiments, thetension, curvature, displacement, or other properties of the tensionmember may be measured. In some embodiments, the position and/or motionof the antenna system may be controlled as it is towed behind the aerialplatform.

In various embodiments, SAR data may be processed to generate a 3D imageand/or mapping of a target surface area. Additionally, various devicesand systems may be utilized to detect, control, and/or compensate forthe curvature and/or displacement of the tension member as it is towedbehind an aerial platform and/or the relative location of antennassecured to the tension member. In addition to SAR processing, theantenna systems and methods described herein may be utilized for a widevariety of spatial signal processing and other radio techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a tension member secured to an aerial platform,including multiple antenna assemblies extending from and spaced alongthe tension member.

FIG. 2 illustrates an exemplary embodiment of a tension membercomprising multiple strands, one or more of which may be used by acommunication system.

FIG. 3A illustrates a winch-style deployment mechanism adapted forin-motion deployment of a tension member.

FIG. 3B illustrates the deployment mechanism with the tension memberpartially deployed.

FIG. 3C illustrates an antenna assembly being selectively secured to thetension member as it is deployed from an aerial vehicle.

FIG. 4 illustrates a plurality of antenna assemblies, each secured to atension member via a mechanism configured to deploy the antennaassemblies from a storage position to a deployed position.

FIG. 5 illustrates a tension member configured with a non-antenna devicefor controlling the location of the second end of the tension memberand/or the shape of the tension member.

FIG. 6 illustrates a propulsion device secured to the second end of thetension member, the propulsion device configured to control the locationof the second end of the tension member and/or shape of the tensionmember.

FIG. 7 illustrates another embodiment of a propulsion device secured tothe second end of the tension member, the propulsion device configuredto control the location of the second end of the tension member and/orshape of the tension member.

FIG. 8 illustrates an example of a propeller device secured to thesecond end of the tension member, the propeller device configured tocontrol the location of the second end of the tension member and/orshape of the tension member.

FIG. 9 illustrates an example of a tension member elevated by anairfoil.

FIG. 10 illustrates a tension member comprising a plurality ofoscillation dampening devices configured to dampen oscillations alongthe tension member.

FIG. 11 illustrates an embodiment of a tension member configured with anon-circular cross section to reduce and/or eliminate twisting and/ordrag.

FIG. 12 illustrates an embodiment of a tension member with a pluralityof curvature detectors spaced along its length.

FIG. 13A illustrates an embodiment of a location system configured todetermine a location of each of a plurality of antenna assemblies alongthe length of a tension member using an imaging device.

FIG. 13B illustrates the embodiment of FIG. 13A, where each of theplurality of antenna assemblies comprises a retroreflector.

FIG. 14 illustrates an embodiment of a location system configured todetermine the location of each of a plurality of antenna assembliesalong the length of a tension member using a local positioning system(LPS) and/or global positioning system (GPS).

FIG. 15 illustrates an embodiment of a location system comprising asonar system configured to determine the location of each of a pluralityof antenna assemblies along the length of a tension member usingreflected radio signals.

FIG. 16 illustrates various possible antenna types that may be securedto a tension member.

FIG. 17 illustrates an embodiment of a plurality of antenna assemblieseach secured to a tension member via an orientation adjustmentmechanism.

FIG. 18 illustrates an alternative aerial platform towing a plurality ofantenna assemblies secured to a tension member.

FIG. 19 illustrates another alternative aerial platform towing aplurality of antenna assemblies secured to a tension member.

FIG. 20 illustrates an embodiment of a plurality of antenna assembliessecured along the length of a tension member secured to an orbitingsatellite.

FIG. 21 illustrates multiple tension members secured to an aerialplatform, each with a plurality of antenna assemblies secured along itslength.

FIG. 22 illustrates an antenna system in use, with an aerial platform inmotion synthesizing a horizontal aperture.

FIG. 23 illustrates a flow chart of a method for using an antenna systemas described herein.

FIG. 24 illustrates a flow chart of a method for using the presentlydescribed antenna system in conjunction with multi-elevational 3D SAR.

DETAILED DESCRIPTION

Some radar techniques, such as synthetic aperture radar (SAR) and otherradio processes, may utilize data gathered from multiple elevationsand/or at multiple locations to determine information about a surface orobject reflecting or emitting a radio frequency (RF) or other signal(s).For example, SAR may be used for ground mapping, object detection,subterranean mapping, sub-foliage mapping, target identification, andthe like. SAR processors may coherently combine amplitude and phaseinformation of electromagnetic energy reflected by a surface. Theelectromagnetic energy may originate from a plurality of sequentiallytransmitted pulses, such as from a transmitter on a moving aerialplatform. A SAR image may be formed from the coherent combination of theamplitude and phase returns from each location the aerial platformtravels. The coherently processed electromagnetic energy allows an imageor mapping to be generated that would be comparable to a system with amuch larger antenna corresponding to approximately the distance traveledby the aerial platform. By combining signals received from multipleelevations, it is possible to generate 3D images or mappings of surfaceareas.

In some embodiments of the presently described systems and methods, anantenna system may be towed by an aerial platform or secured to anorbiting satellite. The antenna system may include a tension member,such as a cable, having a first end and a second end. The first end maybe secured to the aerial platform and the second end may extendunsecured from the aerial platform at a different elevation than thefirst end. A plurality of antennas or antenna assemblies may be securedto and spaced along the length of the tension member. Each antennaassembly includes one or more antennas. Each of the antennas may beadapted for use with a particular frequency or frequency bandwidth. Forexample, each of the antennas may be adapted or tuned to the samefrequency, various frequencies, and/or a frequency bandwidth useful forSAR, other interferometric processes, and/or other radio process. Sincethe second end of the tension member is unsecured to the aerial platformand extends at a different elevation than the first end, each of theantennas may be located at a different elevation relative to the aerialplatform. The length of a tension member may vary based on a particularapplication. For some radio processes (such as SAR and otherinterferometric processes), the tension member may be hundreds or eventhousands of meters long. In other embodiments, the length of thetension member may be a fraction of a wavelength of an associatedantenna's tuned frequency bandwidth. In some embodiments, the tensionmember may be between 2 and 2000 wavelengths of an antenna's tunedfrequency. Thus, depending on the frequency used, the length of thetension member may be several thousand meters. Longer lengths may beuseful in spaceborne applications or as is found useful and practical.

In some embodiments, an antenna system may include multiple tensionmembers, each configured with a plurality of antennas. In such anembodiment, each tension member may be spaced from the other tensionmembers in an in-track (fore and aft) direction, a cross-track (lateralor left to right) direction, and/or at a unique orientation. Theconfiguration of a plurality of antenna assemblies on a tension membermay be configured to receive and/or transmit electromagnetic energy. Theelectromagnetic energy may be transmitted to and/or received from adistinct region (i.e., directed). Additionally or alternatively, each ofthe antenna assemblies may be directed at the same area, overlapping butdistinct areas, and/or completely distinct areas. Thus, a plurality ofantennas associated with a tension member, or even a plurality oftension members, may be configured to operate independently of oneanother or to operate cooperatively. For example, the plurality ofantennas or pluralities of antennas on multiple tension members may beconfigured to operate as a directional array.

In some embodiments, various types of antennas or antenna configurationsmay be used on the same tension member. For example, two different setsof antennas may be configured to operate in two different frequencybands (i.e. one antenna set in each frequency band). In anotherembodiment, two different types of antennas may operate in the samefrequency band, but with a first subset of the antennas operating as lowdirectivity antennas and a second subset of the antennas operating ashigh-gain directional antennas.

The antenna system may receive and/or transmit electromagnetic energyusing the plurality of antennas secured to the tension member at variouselevations. In some embodiments, a receiving system may comprise astorage system and/or a processing system. Accordingly, each of theplurality of antennas may be communicatively connected to a storageand/or processing system via a communication link.

In various embodiments, the antennas in communication with the receivingsystem may be said to be connected via a communication link. Thecommunication link may be relatively simple (e.g., an optical fiber orconductor) or more complex (e.g., a wireless protocol or robustnetwork). For example, the communication link may include one or moreoptical cables extending adjacent to, entwined with, or integrated withthe tension member connecting each of the plurality of antennas to thereceiving system. In some embodiments, the communication link mayutilize an out-of-band wireless network configured to transmitinformation between each of the plurality of antennas and a receivingsystem and/or transmitter. The communication link may include a coaxialcable, a shielded cable, and/or another suitable network cable.

According to various embodiments, the tension member may be constructedof any of a wide variety of materials or combination of materialscapable of providing sufficient support for the plurality of antennaassemblies and the overall length of the tension member itself. Suchmaterials include, but are not limited to, carbon fibers, glass fibers,nylons, metals, polypropylene, polyester, polyethylene, aramids,acrylics, and plastics. The tension member may include a conductivematerial and/or a dielectric material. In some embodiments, the tensionmember may comprise a conductive member divided by a plurality ofinsulating members spaced along the length of the tension member. Insuch an embodiment, the tension member may be divided into a pluralityof segments of electrically conductive material separated from oneanother by an insulating member. In some such embodiments, each of theplurality of segments may be non-resonant to relevant frequencies, so asnot to interfere with a radar process or communications systems. In someembodiments, the tension member may include one or more strands orsub-members.

In some embodiments, a communication system may include an optical cableconnecting each of the plurality of antennas along the length of thetension member to a receiving system and/or transmitter. In someembodiments, the optical cable may extend alongside the tension memberand/or be entwined with strands of the tension member.

According to various embodiments, the tension member may be deployedfrom an aerial platform while the aerial platform is in motion. Forexample, a winch-style mechanism may uncoil a tension member from amoving aerial platform. Each of a plurality of antenna assemblies may beselectively secured to the tension member as the tension member isdeployed. Likewise, each of the plurality of antenna assemblies and/orantennas may be selectively detached from the tension member as thetension member is retracted.

In an alternative embodiment, each of the plurality of antennaassemblies may be secured to the tension member while in a retractedstate. In such an embodiment, as the tension member is deployed, each ofthe plurality of antenna assemblies may extend and/or otherwisetransition to a deployed position with respect to the tension member. Asthe tension member is retracted, each of the plurality of antennaassemblies may retract and/or otherwise transition to a retractedposition (i.e., storage position) with respect to the tension member.

In some embodiments, one or more control devices, such as end masses,airfoils, wings, fins, flaps, drag cones, and/or propulsion devices, maybe used to control the shape of the tension member and/or the locationof the second end of the tension member. In some embodiments, one ormore control devices may be actively driven and/or powered or passivelycontrolled by an airstream. Control devices, receiving systems,transmitters, communication systems, and/or other devices associatedwith an antenna system may be powered using a generator, a turbine, abattery, an optical cable, a free-space optical power system, a powercable extending along or entwined with the tension member, a solarpanel, and/or another mobile power apparatus.

In some embodiments, an electrical conducting cable and/or the tensionmember may comprise a plurality of filters and/or resonant trapsconfigured to divide the electrical conducting cable and/or the tensionmember into a series of electrical lengths configured to not interactelectromagnetically with the antennas within a predetermined frequencybandwidth. For example, a conductive communications cable and/or atension member may include a ferrite core, ferrite components, one ormore inductors, and/or another device capable of forming filters and/orresonant traps. In some embodiments, the electrical conducting cableand/or the communication system may include a coaxial cable.

In some embodiments, the tension member, a connectivity cable of acommunication system, and/or another component within the antenna systemmay include a dampening system configured to dampen mechanicaloscillations. For example, one or more control devices may be positionedalong the length of the tension member to dampen oscillations.

The antenna system may further include an antenna location systemconfigured to determine a location (e.g., an absolute location, anelevation, and/or displacement) of each of the plurality of antennas (orantenna assemblies) relative to the aerial platform, relative to areceiving system, relative to a transmitter, and/or relative to oneanother. Depending on the calculations performed on data collected usingthe plurality of antennas, it may be useful to know the absolute orrelative position (e.g., in-track or cross-track) of each of theplurality of antennas. In one embodiment, an antenna location system mayinclude a curvature sensing optical fiber system configured to determinethe curvature of the tension member at one or more locations along thelength of the tension member. This information, combined with thespacing of each antenna along the tension member of a known totallength, may allow for accurate positional data to be determined for eachof the plurality of antennas. The location of an antenna may be definedwith respect to the phase center of the antenna.

In one embodiment, the antenna location system may be configured toutilize a tension of a tension member, a tensile modulus of the tensionmember, a coefficient of expansion, a temperature of the tension member,an imaging device, electromagnetic illumination (visible or not) (e.g.,flash, strobe, continuous), a reflector, a retroreflector, a globalpositioning system (GPS), a local positioning system (LPS),interferometry of an RF signal, an optical signal, an acoustic orultrasonic signal, inertial sensors, and/or another sensor device todetermine the relative and/or absolute location of each of a pluralityof antennas along a tension member. In some embodiments, the location ofsome of the plurality of antennas may be determined and the location ofthe other antennas may be estimated based on the known location of anend of the tension member and/or the location of some of the pluralityof antennas.

An antenna location system may be configured to utilize the locationand/or spatial orientation of one or more antennas. Location and/orspatial orientation may be determined using optical imaging (includinginfrared or ultraviolet imaging), stereo imaging, RF or microwaveinterferometry, LIDAR or imaging LIDAR (i.e., optical time-of-flightsensing), acoustic or ultrasonic sensing, a Global Positioning System(GPS), differential GPS, or GPS carrier phase sensing, inertial sensing(accelerometers, gyroscopes). The system may utilize known positions ordistances, such as the length of the tension member between two antennaassemblies, and corrections to such known positions or distances, suchas corrections to the length of the tension member based on, e.g.,sensed tension in the tension member and a known tensile modulus of thetension member, or sensed temperature of the tension member and a knowcoefficient of expansion of the tension member. In some embodiments, theeffective location (phase center) of an antenna may be determined atleast in part by measurement of one or more calibration signals receivedor transmitted by the antenna.

One or more of the antennas in an antenna system as described herein maybe an active antenna or a passive antenna. Examples of antennas include,but are not limited to, dipole antennas, Yagi-Uda antennas, hornantennas, planar waveguide antennas, bicone antennas, parabolicreflectors, and/or any other type of antenna capable of receiving and/ortransmitting RF frequencies. The antennas may be configured and/orselected to minimize aerodynamic drag. The plurality of antennas mayinclude various subsets of antennas, where each subset is configured toreceive and/or transmit frequencies within a unique bandwidth. Thebandwidths may comprise single frequencies, narrowband frequency ranges,broadband frequency ranges, or multiple bands of non-contiguousfrequencies.

In some embodiments, the antennas may comprise planar antennas, flatantennas, conformal antennas, flat antennas, and/or the like. Forexample, in one embodiment, electronically steerable antennas may beutilized. The electronically steerable antennas may or may not bephysically steerable. Rather, the antennas may be electronicallycontrollable to adjust the beam angle and/or direction. For example, anantenna may utilize metamaterials surface antenna technology (MSA-T) toform an electronically steerable antenna.

Antennas may be configured to transmit and/or receive a range ofelectromagnetic energy between approximately 10 kilohertz and 300gigahertz. For example, an antenna system may be configured with one ormore antennas configured to receive and/or transmit electromagneticenergy between 3 megahertz and 30 megahertz, 30 megahertz and 300megahertz, 300 megahertz and 3 gigahertz, 3 gigahertz and 30 gigahertz,frequencies within the L-band, S-band, C-band, Ka-band, Ku-band, and/orfrequencies within the X-band. Frequencies may be selected forpenetrating foliage, water, ground, buildings, and/or other obstacles.The antenna system may include a plurality of different antennas,including at least one narrowband antenna, one broadband antenna, and atleast one multi-band antenna.

According to various embodiments, one or more of the plurality ofantenna assemblies may be permanently, semi-permanently, or removablysecured to the tension member. In some embodiments, the plurality ofantenna assemblies may be spaced along the length of a tension member asit is towed by an aerial platform, such that each of the plurality ofantenna assemblies is at a different elevation with respect to theothers. In some embodiments, one or more antenna assemblies may besecured to the tension member via a fixation device configured tocontrol the orientation of an antenna relative to the tension member. Insome embodiments, the fixation device may be passive, such that anairstream may drive the antenna and/or the entire antenna assembly to anorientation with respect to the tension member. In other embodiments,the fixation device may be actively controlled, such as via an actuatorconnected to a power source, to adjust the orientation of an antennarelative to the tension member.

In some embodiments, the orientation of one or more of the antennas maybe dynamically adjusted while being towed by an aerial platform and/orwhile in orbit secured to an orbiting satellite. The orientation of oneor more antennas may be dynamically adjusted relative to the tensionmember, a target surface, a received RF signal, and/or gravity and/orbased on other RF characteristics.

In various embodiments, an antenna system as described herein may beadapted for use with SAR. An antenna system may comprise a plurality ofsub-receiving systems, each configured to receive a signal from one ormore of the antennas in the antenna system. The sub-receiving systemsand/or the receiving system may be located on the aerial platform (orsatellite) or on the tension member. In some embodiments, the receivingsystem may record the information received from each of the plurality ofantennas and associate it with an elevation and/or displacement of theantenna at the time the information was received. Accordingly,information from multiple elevations may be collected using the knowntime, elevation, and/or displacement of the information when it wascollected by each antenna.

Three-dimensional (3D) SAR processing may then be used to create a 3Dmapping or image of a target surface. In an embodiment where the tensionmember hangs straight down, such as a tension member secured to anorbiting satellite, each antenna may collect data at a differentelevation, but at the same relative location to a target surface at anygiven time. In contrast, a tension member towed by an aerial platformmay curve or otherwise be displaced from a straight-down configurationdue to air resistance. By determining the relative location of each ofthe plurality of antennas, including elevation and any left, right,forward, and/or aft displacement, a pre-processor may adjust theinformation received by each of the plurality of antennas to compensatefor the curvature and/or displacement of the tension member.

In some embodiments, processors, pre-processors, SAR devices, and/orother components may be part of the antenna system and/or located on theaerial platform. In other embodiments, a receiving system may simplyrecord the information collected by each of the plurality of antennas,the associated location of each of the antennas, and/or time stamps forthe collected information. In such an embodiment, the recorded data maybe provided or transmitted to remote processing devices.

Any of a wide variety of SAR processing and/or associated dataacquisition techniques may be utilized in conjunction with the presentlydescribed antenna systems and methods. Examples of SAR processing aredescribed in U.S. patent application Ser. No. 08/657,602 filed May 31,1996, now issued as U.S. Pat. No. 5,659,318, which application is herebyincorporated by reference in its entirety.

As previously described, the data collected from each of the pluralityof antennas at varying elevations during a single pass may be adjustedto compensate for any curvature or displacement of the tension member,such that the collected data corresponds to data that would be collectedby a single antenna during multiple passes of an aerial platform.Accordingly, any of a wide variety of 3D synthetic aperture radarimaging processing techniques, including those adapted for multiplepasses of an aerial platform, may be used in combination with thepresently described antenna systems and methods. An example of such amethod is described in She, Z., Gray, D. A., Bogner, R. E., Homer, J., &Longstaff, I. D. (2002) ‘Three-dimensional space-borne syntheticaperture radar (SAR) imaging with multiple pass processing,’International Journal Remote Sensing, 23(20), 4357-82, which is herebyincorporated by reference in its entirety.

As used herein, an aerial platform may include any of a wide variety ofmoving platforms or vehicles. An aerial platform may include any movingplatform, such as airborne and suspended platforms. For example, anaerial platform would include various aircraft and aerial vehicles.Aerial vehicles include, but are not limited to, airplanes, jets,helicopters, lighter-than-air-vehicles, unmanned aerial vehicles (UAVs),rocket-propelled aerial vehicles, and/or other similar vehicles. Anaerial platform may also include any suitable structure extending from amoving and/or pivotable base. For example, a crane or mast mounted on atruck, ship, or other moveable and/or pivotable base, may suspend and/orotherwise support an antenna system as described herein. It will beappreciated that an orbiting satellite may be substituted for an aerialplatform in many, if not all, of the embodiments described herein.

Some of the infrastructure that can be used with embodiments disclosedherein is already available, such as general-purpose computers, computerprogramming tools and techniques, digital storage media, andcommunication links. A computing device may include a processor such asa microprocessor, microcontroller, logic circuitry, or the like. Theprocessor may include a special purpose processing device such asapplication-specific integrated circuits (ASIC), programmable arraylogic (PAL), programmable logic array (PLA), programmable logic device(PLD), field programmable gate array (FPGA), or other customizableand/or programmable device. The computing device may also include amachine-readable storage device such as non-volatile memory, static RAM,dynamic RAM, ROM, CD-ROM, disk, tape, magnetic, optical, flash memory,or other machine-readable storage medium. Various aspects of certainembodiments may be implemented using hardware, software, firmware, or acombination thereof.

The embodiments of the disclosure will be best understood by referenceto the drawings, wherein like parts are designated by like numeralsthroughout. The components of the disclosed embodiments, as generallydescribed and illustrated in the figures herein, could be arranged anddesigned in a wide variety of different configurations. Furthermore, thefeatures, structures, and operations associated with one embodiment maybe applicable to or combined with the features, structures, oroperations described in conjunction with another embodiment. In otherinstances, well-known structures, materials, or operations are not shownor described in detail to avoid obscuring aspects of this disclosure.

Thus, the following detailed description of the embodiments of thesystems and methods of the disclosure is not intended to limit the scopeof the disclosure, as claimed, but is merely representative of possibleembodiments. In addition, the steps of a method do not necessarily needto be executed in any specific order, or even sequentially, nor do thesteps need to be executed only once.

FIG. 1 illustrates an antenna system, including a tension member 150secured to an aerial platform 100. A plurality of antenna assemblies151, 152, 153, and 154 are secured to and spaced along the tensionmember 150. Each antenna assembly may include at least one antenna forreceiving and/or transmitting electromagnetic energy. In variousembodiments, the antenna system may include a transmitter 110 configuredto transmit an RF signal toward a target area on a surface 195. Invarious embodiments, the RF signal may be reflected by the surface 195and/or other objects, such as a structure 190, and received by one ormore of the antenna assemblies 151-154.

As illustrated, a first end of the tension member 150 may be secured tothe aerial platform 100, such that the tension member 150 is configuredto be towed by the aerial platform 100. The second end of the tensionmember 150 may be unsecured to the aerial platform, as illustrated. Asthe aerial platform 100 moves forward, air friction may displace thesecond end of the tension member 150 and/or cause the tension member 150to curve slightly, as illustrated.

Throughout the drawings, the proportions and relative sizes of objects,features, and components may not be drawn to scale. For example, eachantenna assembly 151-154 may be relatively small compared to the aerialplatform 100 and/or the total length of the tension member 150. In someembodiments an antenna assembly 151-154 may include an antenna with alength between a quarter of a wavelength and a wavelength of a selectedfrequency, and the tension member 150 may have a length between ¼ and2000 wavelengths of the selected frequency. In various embodiments, oneor more of the antenna assemblies 151-154 may be configured for use withfrequencies useful for radio communications, radiolocation, and/orradar. For example, the system may be useful for one or more types ofsynthetic aperture radar. As each of the antenna assemblies 151-154 islocated at a different elevation, the antenna system depicted in FIG. 1may be used to collect SAR data from multiple elevations using a singlepass of the aerial platform 100 over a target area of the surface 195.Alternatively, multiple passes of the aerial platform 100, each atdifferent elevations, may result in an even greater number of SAR datapoints at numerous elevations.

In some embodiments, each of the antenna assemblies 151-154 may beconfigured to receive (and/or transmit) an RF signal reflected by thesurface 195 and/or the structure 190 and convey the collectedinformation to a receiving system. The receiving system may be part ofthe antenna system and secured to the tension member 150, oralternatively located within the aerial platform 100. In variousembodiments, a communication link may relay information from each of theplurality of antennas to the receiving system. In some embodiments, thereceiving system may simply store the received information. In otherembodiments, the receiving system may relay the information to a remotelocation and/or be used to transfer the information to a remoteprocessing unit.

A SAR processor, such as a 3D SAR processor, may utilize the informationcollected from multiple elevations to generate a mapping, an image,and/or a rendering of the surface 195 and/or the structure 190. Bycollecting data from multiple elevations using a single pass of theaerial platform 100, a 3D mapping, image, and/or rendering of thestructure 190 may be possible without the necessity of multiple passes.Moreover, using a single pass of an aerial platform 100 while collectingdata from multiple elevations reduces the likelihood that objects on thesurface 195 will move before subsequent passes can be performed, as islikely in systems configured for multi-pass elevational SAR datacollection.

Each of the plurality of antenna assemblies 151-154 may be adapted foruse (receiving and/or transmitting) with particular frequencies orfrequency bandwidths. For example, the antenna assemblies 151-154 may beconfigured to transmit and/or receive a range of frequencies betweenapproximately 10 kilohertz and 300 gigahertz. For example, an antennasystem may be configured with one or more antenna assemblies 151-154configured to receive and/or transmit frequencies between 3 megahertzand 30 megahertz, 30 megahertz and 300 megahertz, 300 megahertz and 3gigahertz, 3 gigahertz and 30 gigahertz, frequencies within the L-band,S-band, C-band, Ka-band, Ku-band, and/or frequencies within the X-band.Frequencies may be selected for penetrating foliage, water, ground,buildings, and/or other obstacles.

FIG. 2 illustrates an exemplary embodiment of a tension member 250comprising multiple strands 210 and 220. According to variousembodiments, the tension member 250 may be constructed of any of a widevariety of materials or combination of materials capable of providingsufficient support for the plurality of antenna assemblies and theoverall length of the tension member itself. Such materials include, butare not limited to, carbon fibers, glass fibers, nylons, metals,polypropylene, polyester, polyethylene, aramids, acrylics, and plastics.The tension member 250 may include a conductive material 210 and/or adielectric material 220.

In some embodiments, the tension member may comprise a conductive memberdivided by a plurality of insulating members spaced along the length ofthe tension member, such that the tension member is divided into aplurality of segments of electrically conductive material separated fromone another via an insulating member. Each of the plurality of segmentsmay be non-resonant to relevant frequencies.

As illustrated, the tension member 250 may include a plurality ofentwined strands 210 and 220. The entwined strands 210 and 220 may bebraided, woven, twisted, and/or fused together. One or more of thestrands may be integral to the communication system configured toconnect one or more antennas (or antenna assemblies) secured to thetension member 250 to a receiving system on an aerial platform. Forexample, one or more of the conductive strands 210 may be configured totransmit electrical signals from secured antennas to a receiving system.Alternatively, the dielectric strands 220 may include an optical fiberconfigured to transmit information from secured antennas to a receivingsystem. One or more of the strands 210 and 220 may comprise a coaxialcable, a shielded cable, and/or another transmission medium suitable fordata transmission.

FIG. 3A illustrates a winch-style deployment mechanism 375 for deployinga tension member 350 prior to an aerial platform 311 moving or while anaerial platform 311 is in motion. The illustrated embodiment includesthe tension member 350 coiled around a drum of the deployment mechanism375. As illustrated, the antenna assemblies have been removed from thetension member 350; however, in some embodiments, the antenna assembliesmay remain secured to the tension member 350 in a storage (retracted)position while the tension member 350 is in a retracted position.

FIG. 3B illustrates the tension member 350 partially deployed as it isunwound from the drum of the deployment mechanism 375 attached to theaerial platform 311. As illustrated, the tension member 350 may passthrough an antenna assembly attachment device 383. The antenna assemblyattachment device may be configured to selectively attach one or moretypes of antennas and/or antenna assemblies to the tension member 350 asit is deployed from the aerial platform 311.

FIG. 3C illustrates an antenna assembly 354 being secured to the tensionmember by the antenna assembly attachment device 383 as the tensionmember 350 is deployed from the aerial vehicle 311 via the deploymentmechanism 375. The antenna assemblies may be secured to and spaced apartfrom each other along the tension member 350 according to any of a widevariety of arrangements. The deployment mechanism 375 may be used todeploy the tension member 350 from any of a wide variety of aerialplatforms, including, but not limited to, airplanes, jets, helicopters,lighter-than-air-vehicles, unmanned aerial platforms (UAPs),rocket-propelled vehicles, and/or other similar vehicles. As in otherembodiments, the dimension and sizes of various components in thedrawings may be exaggerated in order to show details of the presentlydescribed system and methods. For instance, the length of the tensionmember 350 may be significantly longer than suggested by theillustrations. According to various embodiments, antenna assemblies 354may be secured to the tension member 350 while it is being deployedand/or after it has been fully deployed from the aerial vehicle 311.Similarly, one or more communication cables for connecting the antennaassemblies to a receiving system may be secured to, entwined with,and/or deployed along the length of the tension member during orfollowing deployment.

The deployment mechanism 375 may be used to deploy the tension member350 from any of a wide variety of aerial platforms and/or space craft,including, but not limited to, orbiting satellites, orbiting spacecraft, airplanes, jets, helicopters, lighter-than-air-vehicles, unmannedaerial platforms (UAPs), rocket-propelled vehicles, and/or other similarvehicles.

FIG. 4 illustrates an antenna system configured with a plurality ofantenna assemblies 451, 452, 453, and 455. Each of the antennaassemblies 451-454 may be secured to a tension member 450. Asillustrated, at least some of the antenna assemblies 451-454 may besecured to the tension member 450 via a mechanism 461, 462, 463, and464. The mechanisms 461-464 may be configured to pivot, or otherwisetransition, each of the antenna assemblies 451-454 (or just theassociated antennas) with respective to a pivot point 471, 472, 473, 474and relative to the tension member 450. The mechanism 461-464 may allowthe antenna assemblies 451-454 to be stored or retracted when thetension member 450 is retracted, rather than being removed. In someembodiments, the mechanisms 461-464 may comprise a spring, otherresilient member, and/or a pneumatic device.

For example, as a winch-style deployment mechanism, such as thosedepicted in FIGS. 3A-3D, deploys the tension member 450, each of theantenna assemblies 451-454 may pivot about their respective pivot points471-474 to transition from a storage position to a deployed position.Similarly, as the tension member 450 is retracted, each of the pluralityof antenna assemblies 451-454 may retract and/or otherwise transition toa retracted position (i.e., storage position) with respect to thetension member 450.

FIG. 5 illustrates an antenna system towed by an aerial platform 500,including a tension member 550 configured with an end mass 575 adaptedto control the location of the second end of the tension member 550and/or shape the tension member 550. Any number of antennas and/orantenna assemblies may be secured along the length of the tension member550, including antenna assemblies 551 and 552 as illustrated. The endmass 575 may provide a weight at the second end of the tension member550 to cause the tension member 550 to hang more vertically and/ordecrease the amount of curvature due to air friction as the aerialplatform 500 travels. Dashed line 550′ represents a possible curvatureand location of the second end of the tension member 550 if end mass 575were not present.

As previously described, the presently described systems and methodsprovide a means to collect information from multiple antennas atmultiple elevations with a single pass of an aerial platform. In variousembodiments, it may be useful or necessary to adjust the informationreceived by each of the antennas based on displacement of the antenna indirections other than elevation due to air friction. The end mass 575may cause the tension member 550 to hang more vertically from aerialplatform 500, eliminating the need to adjust and/or reducing the degreeto which the information is adjusted due to antenna displacement.

FIG. 6 illustrates a propulsion device 675 secured to the second end ofa tension member 650. The propulsion device 675 may control the locationof the second end of the tension member 650 and/or shape the tensionmember 650. Additional propulsion devices 675 may be located anywherealong the length of the tension member 650 to further shape the tensionmember 650. In the illustrated embodiment, the propulsion device 675 isconfigured to drive the second end of the tension member 650 above theaerial platform 600. Each of the antenna assemblies 651 and 652, andother additional antenna assemblies and/or antennas, may be securedalong the length of the tension member 650 at varying elevations.Accordingly, each of the antenna assemblies 651 and 652 may receive anRF signal transmitted by transmitter 610 and reflected by a surface 695and/or a structure 690 at a different elevation. Using the datacollected at multiple elevations, 3D SAR, or other radio signal,processing may be performed using a single pass of an aerial platform.

FIG. 7 illustrates another embodiment of a propulsion device 775, inwhich the propulsion device 775 is secured to the second end of thetension member 750 and configured to shape the tension member 750 morevertically downward. Again, the propulsion device 775 may be configuredto control the location of the second end of the tension member 750and/or shape the tension member 750.

FIG. 8 illustrates an example of a propeller device 875 secured to thesecond end of the tension member 850. The propeller device 875 may beconfigured to control the location of the second end of the tensionmember 850 and/or shape the tension member 850. Any of a wide variety oftension member shaping and/or tension member location control devicesmay be employed, including any combination of end masses, airfoils,wings, fins, flaps, drag cones, and/or propulsion systems. Such controldevices may be positioned along the tension member 850 and/or secured tothe second end thereof. The control devices may be passive, such as anend mass, and/or actively powered/controlled, such as a propulsionsystem. Some control devices, such as the propeller device 875, may beactively powered and/or passively driven by a passing airstream. Controldevices, receiving systems, transmitters, communication systems, and/orother devices associated with an antenna system may be powered using agenerator, a turbine, a battery, an optical cable, a free-space opticalpower system, a power cable extending along or entwined with the tensionmember, a solar panel, and/or another mobile power generating apparatus.

FIG. 9 illustrates an example of an antenna system including a tensionmember 950 suspended by an airfoil 983 above the aerial platform 900.The airfoil 983 may control the location of the end of the tensionmember 950 and/or shape the tension member 950. Additional airfoils maybe located anywhere along the length of the tension member 950 tofurther shape the tension member 950. In the illustrated embodiment, theairfoil 983 is configured to drive the second end of the tension member950 above the aerial platform 900. Each of the antenna assemblies 951,952, 953, and 954 and/or other additional antenna assemblies and/orantennas, may be secured along the length of the tension member 950 atvarying elevations.

A receiving system may receive, store, and/or process theelectromagnetic energy received by the antennas in the antennaassemblies 951-954. According to various embodiments, any of a widevariety of signal processing systems and/or methods may be utilized inconjunction with the presently described antenna systems, including, butnot limited to, SAR and 3D SAR techniques. In various embodiments, thesignals received by each of a plurality of antennas secured at variouselevations along a towed tension member may be adjusted to compensatefor curvature and/or any displacement of the tension member, such thatthe signals effectively represent data collected at the same co-planarlocation relative to a target surface, but at multiple elevations. Usingthe collected data, any of a wide variety of 3D SAR techniques,including those adapted for multiple passes of an aerial platform, maybe used in combination with the presently described antenna systems andmethods.

FIG. 10 illustrates an antenna system, including a tension member 1050towed by an aerial platform 1000. As illustrated, a plurality of antennaassemblies 1051, 1052, 1053, and 1054 may be secured to, spaced apartfrom each other, and extend from the tension member 1050. As previouslydescribed, the tension member 1050 may be between a few wavelengths andseveral thousand wavelengths long. That is, using a frequency between 3megahertz and 3 gigahertz, the tension member 1050 may be up to tens orhundreds of meters long, or in some cases even several thousand meterslong. Accordingly, one or more oscillation dampening devices 1075 may besecured along or in-line with the tension member 1050. Any of a widevariety of oscillation dampening devices may be utilized, as arecommonly known in the art. In some embodiments, the oscillationdampening devices may comprise passive dampening devices. Theoscillation dampening devices may also comprise activelycontrolled/powered dampening devices.

FIG. 11 illustrates an embodiment of a section of a tension member 1110configured with a rounded front 1157 and a tapered rear 1155. Accordingto such an embodiment, a tension member 1110 configured with a roundedfront 1157 and/or a tapered rear 1155 may reduce air friction and/orreduce or eliminate twisting of the tension member 1110 during use. Anyof a wide variety of shapes, dimples, divots, grooves, fins, foils,and/or other aerodynamic characteristics may be used to reduce theaerodynamic drag of a tension member, antenna, communication system,receiving system, and/or transmitter. In some embodiments, it may bedesirable to reduce air drag as much as possible in order for thetension member to hang as close as possible to straight down from anaerial platform and/or to minimize the propulsive power required by theplatform.

FIG. 12 illustrates an embodiment of an antenna system towed by anaerial platform 1200, including a tension member 1250, a plurality ofantenna assemblies 1251, 1252, 1253, and 1254 and an antenna locationsystem. Accurate elevational data for each of the plurality of antennasassociated with each of the antenna assemblies 1251-1254 may be usefulfor performing various calculations, including those associated withradio communication, radiolocation, and/or radar techniques, such as 3DSAR. In the illustrated embodiment, the antenna location systemcomprises a plurality of curvature detectors 1261, 1262, 1263, 1264,1265, 1266, 1267, and 1268, spaced along the length of the tensionmember 1250. In various embodiments, the sensors 1261-1268 may becoincident with antenna assemblies 1251-1254 and some of the sensors1261-1268 may be spaced between the antenna assemblies 1251-1254. One ormore of the sensors may be configured to sense or determine a curvature,temperature, tension, strain, and/or another property of the tensionmember 1250.

According to various embodiments, each of the curvature detectors1261-1268 may be configured to determine the amount of curvature of thetension member 1250 at a given point, or at all points. Using a knownlength of the tension member 1250, a known position of each of theplurality of antennas associated with each of the antenna assemblies1251-1254, and the detected curvature, a relative elevation of each ofthe plurality of antenna assemblies 1251-1254 may be determined. Thecurvature detectors 1261-1264 may comprise a curvature sensing fiberoptic sensor extending along at least a portion of the length of thetension member 1250.

FIG. 13A illustrates another embodiment of an antenna system including atension member 1350, a plurality of antenna assemblies 1351, 1352, 1353,and 1354, and an antenna location system. In the illustrated embodiment,an imaging device 1310 may optically determine the location of each ofthe antennas associated with each of the plurality of antenna assemblies1351-1354. In some embodiments, the imaging device may include anartificial light source 1320, such as a flash, to enhance the image andallow for improved location determination of each of the antennasassociated with each of the plurality of antenna assemblies 1351-1354.The imaging device 1310 and/or associated processing device may utilizeany of a wide variety of imaging detection techniques, includingauto-focusing techniques, such as contrast detection, phase detectionfocusing, and image analysis techniques such as object detection, edgedetection, and/or other image analysis techniques, to determine arelative location of each of the plurality of antennas associated witheach of the plurality of antenna assemblies 1351-1354. In someembodiments, the imaging device 1310 may determine a curvature of thetension member 1350 and then the antenna location system may calculatethe location (displacement and/or elevation) of each of the plurality ofantennas using that information.

FIG. 13B illustrates an embodiment similar to that of FIG. 13A, in whicheach of the plurality of antenna assemblies 1351-1354 includes areflector or retroreflector 1375. The artificial light source 1320 maytransmit light to each of the retroreflectors 1375. The light may returnfrom the retroreflectors 1375 to the imaging device 1310 and facilitatein the determination of the location of each of the plurality ofantennas. The concept of “determining the location” of an antenna orantenna assembly, as used herein, may relate to determining the physicallocation of some portion of an antenna or antenna assembly, such as aconnection point, endpoint, midpoint, etc., and/or to a phase center ofan antenna.

FIG. 14 illustrates another embodiment of an antenna system towed by anaerial platform 1400, including a tension member 1450, a plurality ofantenna assemblies 1451, 1452, 1453, 1454, and 1455, and an antennalocation system. In the illustrated embodiment, the antenna locationsystem may include a processing device (not illustrated) that receivesinformation (such as a time stamp) from a local positioning system (LPS)device or global positioning system (GPS) device 1453 secured adjacentto, near, or to each of the antennas 1451-1455. Using the receivedinformation, the antenna location system may determine the relativelocation of each of the plurality of antennas associated with each ofthe antenna assemblies 1451-1455. Receivers may be located in one ormore locations to receive information from the LPS, such as receivers1460 and/or 1461. Multiple receivers (e.g., 3 or more) may be used foraccurate triangulation of a location. Transmitters (pseudolites) 1460,1461 may be placed in two or more locations to supply signals for alocal positioning system. Three or more transmitters may be used toallow full three-dimensional locating. Alternatively, in someembodiments, devices 1455 may be transmitters of the LPS signal, whiledevices 1460, 1461 may be LPS receivers.

FIG. 15 illustrates another embodiment of an antenna system towed by anaerial platform 1500, including a tension member 1550, a plurality ofantenna assemblies 1551, 1552, 1553, 1554, and 1555, and an antennalocation system. In the illustrated embodiment, the antenna locationsystem may utilize an RF transceiver to emit a radio signal (out-of-bandrelative to the antennas tuning) that is reflected by the antennas1551-1555. By measuring the timing, incident direction, and/or phase ofthe returning RF signals, the location of each of the antennas of eachof the antenna assemblies 1551-1555 may be determined. Antennas1551-1554 may incorporate RF retroreflectors or transponders to increasethe returned signal and to provide a known location for the point ofreflection. Alternatively, in some embodiments, acoustic (audible orultrasonic) signals may be used in place of RF signals. In someembodiments, the acoustic signals may be corrected for Doppler shift dueto the motion of the platform through the air.

FIGS. 12-15 illustrate various examples of antenna location systems. Anyof a wide variety of antenna location systems and methods may be used incombination or alone, including those utilizing a measured or determinedtension of a tension member, a tensile modulus of the tension member, acoefficient of expansion, a temperature of the tension member, animaging device, artificial light, a reflector, a retroreflector, aglobal positioning system (GPS), a local positioning system (LPS),interferometry of a radio frequency (RF) signal, an optical signal,laser scanning system, inertial sensors, and/or another sensor device todetermine the relative and/or absolute location of each of a pluralityof antennas (and/or antenna assemblies) along a tension member. In someembodiments, the location of some of the plurality of antennas may bedetermined and the location of the other antennas may be estimated basedon the known location of an end of the tension member, a known length ofa tension member, and/or the location and/or spacing of some of theplurality of antennas.

FIG. 16 illustrates a variety of possible antenna types attached to atension member 1650, which is deployed from a platform 1600. An antenna1651 is a dipole antenna parallel to the tension member 1650, whichmight be physically integrated into or onto the tension member, e.g., bytaping, gluing, etc. the antenna conductors to the tension member. Theantenna 1652 is a vertically-oriented dipole antenna mounted directly tothe tension member 1650. An antenna 1653 is a pair of crossed dipoles,suitable for transmitting or receiving any polarization (e.g.,horizontal, vertical, diagonal, circular) attached to the tension member1650 by a feed element 1654. The antenna 1655 is a wire bicone antenna,similar to dipole 1652 but having broader bandwidth. The antenna 1656 isa Yagi (or Yagi-Uda) multi-element antenna, oriented cross-track. Unlikethe antennas listed above, this antenna will preferentially receivesignals from one side of the platform's track. The antenna 1657 is athin flat panel antenna, such as a patch radiator antenna, mounted on arigid panel. The antenna 1658 is a thick flat panel antenna, such as anactive phased array antenna, mounted in an airfoil-shaped housing forreduced aerodynamic drag. Finally, the antenna 1659 is an example of anantenna assembly comprising a flat panel antenna 1660, such as asteerable metamaterial antenna, supported at an angle to vertical. Suchantenna configurations are commonly used for radars intended to view theground close to the ground track of the aerial platform.

FIG. 17 illustrates an embodiment of a plurality of antenna assemblies1751, 1752, and 1753 each secured to a tension member 1750. The antennaassemblies 1751 and 1752 may be secured to the tension member via theorientation adjustment mechanisms 1765 and 1767. As the tension member1750 is towed by an aerial platform 1700, the orientation of the antennaassemblies and/or associated antennas 1751 and 1752 may be adjustedrelative to the tension member 1750, a surface 1795, and/or the aerialplatform 1700. In some embodiments, an RF signal transmitted by atransmitter 1710 may be reflected by a structure 1790 and then receivedby the antenna assemblies 1751-1753. The orientations of the antennaassemblies 1751 and 1752 may be dynamically adjusted via the orientationadjustment mechanisms 1765 and 1767 to optimize the reception of thedesired/selected reflected signal(s).

The orientation, angle, or other antenna property, such as a length, maybe dynamically adjusted to vary an RF characteristic, such as apolarization, resonant frequency, or mutual coupling between adjacentantennas. Any of a wide variety of alternative control and deploymentdevices may be utilized in conjunction with the presently describedantenna assemblies secured to a tension member. For example, springs,hydraulics, and/or other control devices may be used to adjust theorientation of an antenna assembly and/or an associated antenna withrespect to the ground, the aerial platform, and/or the tension member.The orientation of one or more of the antenna assemblies may bedynamically adjusted while being towed by an aerial platform. Theorientation of one or more antenna assemblies may be dynamicallyadjusted relative to the tension member, a target surface, a received RFsignal, and/or gravity and/or based on other RF characteristics.

FIG. 18 illustrates an alternative aerial platform, a helicopter 1800,towing a plurality of antenna assemblies 1851, 1852, 1853, and 1854secured to a tension member 1850. Similarly, FIG. 19 illustrates anotheralternative aerial platform, a lighter-than-air vehicle 1900, towing aplurality of antennas 1951, 1952, 1953, and 1954 secured to a tensionmember 1950. In some embodiments, the lighter-than-air-vehicle 1900 maybe propeller driven, or otherwise powered. An embodiment of the antennasystem described herein may be particularly suited for applications withlighter-than-air-vehicles 1900 that are only capable of single pass(e.g., as driven by the wind), as the antenna system may be able tocollect data from multiple elevations during the single pass. In someembodiments, the lighter-than-air-vehicle 1900, the antenna assemblies1951-1954, and the tension member may be expendable. In such instances,the data collected by the antenna assemblies 1951-1954 may be stored forsubsequent retrieval and/or transmitted to a remote receiver.

FIG. 20 illustrates an embodiment of an antenna system configured to besecured to a space vehicle, such as an orbiting satellite 2000. In theillustrated embodiment, a tension member 2050 may extend from theorbiting satellite toward a surface 2095. A plurality of antennaassemblies 2051, 2052, 2053, 2054, and 2055 may be secured along thelength of the tension member 2050. The various systems, methods,components, location systems, communication systems, receiving systems,transmitters, and the like may be used in conjunction with the antennasystem secured to an orbiting satellite 2000, as may be readilyappreciated.

FIG. 21 illustrates multiple tension members 2150 and 2170 secured to anaerial platform 2100. In the illustrated embodiment, the antenna systemmay include two tension members 2150 and 2170, each with a plurality ofantenna assemblies 2151-2154 and 2171-2174 secured along theirrespective lengths. Each tension member 2150 and 2170 and theircorresponding plurality of antenna assemblies 2151-2154 and 2171-2174may perform any of the various functions described herein. Similarly,any of the various systems, methods, devices, and/or features describedin conjunction with a single tension member may be equally applied to adual- or multi-tension member antenna system.

As illustrated, each tension member 2150 and 2170 may be spaced apart.In various embodiments, a plurality of tension members may be spacedapart in an in-track direction, in a cross-track direction (asillustrated), and/or at a unique orientation. Each tension member 2150and 2170 may be configured to receive electromagnetic energy from and/ortransmit electromagnetic energy to a distinct area of a target surface2195, the same area of a target surface 2195, and/or overlapping areasof a target surface 2195.

FIG. 22 illustrates a tension member 2250 with a plurality of antennaassemblies secured along its length (not labeled for clarity) for use insynthetic aperture radar. As illustrated, electromagnetic energy 2270′may be continuously or intermittently transmitted from an aerialplatform as it moves from location 2200′ to location 2200. Reflectedsignals 2275 may be received by each of the plurality of antennasassociated with each antenna assembly at distinct elevations as theaerial platform moves from location 2200′ to location 2200.

The reflected signals 2275 received by the multi-elevational antennasmay be transmitted by a communication system to a receiving system,recorder, and/or SAR processor. In some embodiments, SAR processing, orother type of processing associated with any type of radiocommunication, radiolocation, and/or radar technique may be done inreal-time. In other embodiments, processing may be performedsubsequently using recorded data. Each received reflected signal 2275may be associated with a time stamp of when it was received, a locationof where the antenna was when it was received, a curvature of thetension member 2250 when it was received, and/or the elevation of theantenna when it was received. This information may be thought of ascorresponding to a received signal at multiple elevations for eachlocation between 2200′ and 2200, or the equivalent of data collected bymultiple passes of an aerial platform with a single-elevation antennacollecting SAR data.

Suitable embodiments of the antenna system may be used to implement anyof a wide variety of radar remote sensing and/or imaging techniques,including particularly three-dimensional stereo or “multi-pass” SAR andinterferometric SAR. Embodiments may be optimized for particular sensingor imaging techniques, for example by selecting vertical spacingsbetween antennas to provide a desired set of interferometric or stereoimaging baselines. Embodiments of the antenna system can implementpolarimetric and interferometric radars, multiband, wideband, andultrawideband radars, impulse, chirped-pulse, or phase-encoded radars,foliage- or ground-penetrating radars, moving-target indicating radars,and many other types of radar. Embodiments of the antenna arepotentially compatible with any radar or SAR processing techniqueapplicable to single- or multi-pass data collection, including variousimage-forming techniques (Fourier, back-projection, etc.), autofocustechniques, resolution enhancement or superresolution techniques,speckle reduction techniques, and so on. Some embodiments may beoptimized for specific processing techniques, for example by maintaininguniform vertical spacings and/or uniform horizontal offsets betweenantennas to simplify Fourier-transform processing.

FIG. 23 illustrates a flow chart of a method 2300 for using an antennasystem as described herein. As will be appreciated by one of skill inthe art, various steps of the method may be performed out of order ormore than once with respect to one or more of the other steps. Asillustrated, a transmitter may be used to transmit an RF signal toward atarget surface, at 2310. An aerial platform may be used to tow a tensionmember, at 2320. As described herein, any number of antennas and/orantenna assemblies may be secured along the length of the tension memberat varying elevations. The transmitted RF signal may reflect off thetarget surface.

Each of the plurality of antennas at the varying elevations may receiveportions of the reflected RF signal, at 2330. An antenna location systemmay determine the relative location (e.g., an elevation and/or adisplacement) of each of the antennas and/or antenna assemblies, at2340. A receiving system may receive, process, and/or record informationassociated with the received electromagnetic energy from each of theantennas, at 2350. For example, information associated with the actualreceived signal, a time stamp, a location of the antenna, a curvature ofthe tension member, an elevation of the antenna, and/or the like may berecorded, used for processing, and/or otherwise received by thereceiving system.

FIG. 24 illustrates a flow chart of a more specific method 2400 of usefor the presently described antenna system. As illustrated, atransmitter may transmit a coherent RF signal toward a target surface,at 2410. An aerial platform (or alternatively an orbiting satellite) maybe used to tow a tension member, at 2420. Again, any number of antennasand/or antenna assemblies may be secured along the length of the tensionmember at varying elevations. The transmitted RF signal may reflect offthe target surface.

Each of the plurality of antennas at the varying elevations may receiveportions of the reflected RF signal, at 2430. An antenna location systemmay determine the relative location (e.g., an elevation and/or adisplacement) of each of the antennas and/or antenna assemblies, at2440. A receiving system may receive and/or record informationassociated with the received electromagnetic energy from each of theantennas, at 2450. For example, information associated with the actualreceived signal, a time stamp, a location of the antenna, a curvature ofthe tension member, an elevation of the antenna, and/or the like may berecorded and/or otherwise received by the receiving system.

The information may be pre-processed before storage, pre-processed inreal-time by a SAR processer, and/or subsequently pre-processed tocompensate for any curvature of the tension member and/or lateral (e.g.,forward, aft, left, right) displacement of the tension member, at 2460.A real-time processor on the aerial platform, a real-time remoteprocessor, and/or a subsequently used remote processor may process thepre-processed information using any one of the various SAR techniquesdescribed herein and/or another SAR technique to generate a 3D mappingof the target surface, at 2470.

This disclosure has been made with reference to various exemplaryembodiments, including the best mode. However, those skilled in the artwill recognize that changes and modifications may be made to theexemplary embodiments without departing from the scope of the presentdisclosure. While the principles of this disclosure have been shown invarious embodiments, many modifications of structure, arrangements,proportions, elements, materials, and components may be adapted for aspecific environment and/or operating requirements without departingfrom the principles and scope of this disclosure. These and otherchanges or modifications are intended to be included within the scope ofthe present disclosure.

The foregoing specification has been described with reference to variousembodiments. However, one of ordinary skill in the art will appreciatethat various modifications and changes can be made without departingfrom the scope of the present disclosure. Accordingly, this disclosureis to be regarded in an illustrative rather than a restrictive sense,and all such modifications are intended to be included within the scopethereof. Likewise, benefits, other advantages, and solutions to problemshave been described above with regard to various embodiments. However,benefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, a required, or anessential feature or element. The scope of the present invention should,therefore, be determined by the following claims.

What is claimed is:
 1. A system for generating a three-dimensionalmapping of a target surface using synthetic aperture radar (SAR) datacollected by a single pass of an aerial platform, comprising: atransmitter configured to transmit coherent electromagnetic radiation toa target surface; a tension member configured with a first end and asecond end defining a length of the tension member, the first endconfigured to be secured to an aerial platform and the second endconfigured to be unsecured to the aerial platform and extend from theaerial platform at a different elevation than the first end; a pluralityof antenna assemblies secured to and spaced along the length of thetension member, each of the plurality of antenna assemblies comprisingat least one antenna configured to receive the coherent electromagneticradiation reflected by the target surface; an antenna location systemconfigured to determine a relative location of each of the plurality ofantennas; a receiving system configured to receive informationassociated with the received coherent electromagnetic radiation fromeach of the plurality of antennas; a communication link configured tocommunicatively connect each of the plurality of antennas to thereceiving system, such that information may be conveyed from each of theplurality of antennas to the receiving system with the coherencypreserved; and a processor configured to process the receivedinformation associated with the coherent electromagnetic radiation usinga synthetic aperture radar technique to generate a three-dimensionalmapping of at least a portion of the target surface.
 2. The system ofclaim 1, wherein the plurality of antennas are configured to form amultistatic configuration with at least one external component.
 3. Thesystem of claim 1, wherein each of the plurality of antenna assembliesis secured to and spaced along the length of the tension member atnon-uniform intervals.
 4. The system of claim 1, wherein the pluralityof antenna assemblies are secured to and spaced along the length of thetension member at intervals that correspond to desired elevationalspacings.
 5. The system of claim 1, wherein the information associatedwith the received electromagnetic energy received by the receivingsystem comprises phase information associated with the receivedelectromagnetic energy received by each of the plurality of antennas. 6.The antenna system of claim 1, wherein the transmission from each of theplurality of antennas to the receiving system preserves the timecoherence of the received electromagnetic energy.
 7. The system of claim1, wherein the length of the tension member is between 2 meters and 2000meters.
 8. The antenna system of claim 1, further comprising at leastone non-antenna component secured to the tension member.
 9. The systemof claim 8, further comprising a control device configured to control alocation of at least one of a plurality of points along the tensionmember relative to the aerial platform.
 10. The system of claim 1,wherein the antenna location system comprises a curvature sensingoptical fiber system configured to provide information indicating thecurvature of the tension member at at least one location along thelength of the tension member.
 11. The system of claim 1, wherein theantenna location system is configured to utilize a local positioningsystem (LPS) to determine the relative location of each of the pluralityof antennas.
 12. The system of claim 1, wherein at least one of theplurality of antennas comprises a passive antenna.
 13. The antennasystem of claim 1, wherein at least one of the plurality of antennascomprises a flat antenna.
 14. The antenna system of claim 1, wherein atleast one of the plurality of antennas comprises a conformal antenna.15. The antenna system of claim 1, wherein at least one of the pluralityof antennas comprises an electronically steerable antenna, configuredsuch that the physical antenna remains in a fixed form while a beamangle of the physical antenna is electronically steerable.
 16. Thesystem of claim 1, wherein at least one of the plurality of antennas isconfigured for use with a subset of frequencies between approximately 3megahertz and 30 megahertz.
 17. The system of claim 1, wherein at leastone of the plurality of antennas is configured for use with frequenciesbetween approximately 30 megahertz and 300 megahertz.
 18. The system ofclaim 1, wherein at least one of the plurality of antennas is configuredfor use with frequencies between approximately 300 megahertz and 3gigahertz.
 19. The system of claim 1, wherein the plurality of antennasincludes multiple types of antennas.
 20. The system of claim 19, whereinthe types of antennas are selected from the group of antenna typesconsisting of dipole antennas, Yagi-Uda antennas, horn antennas, planarwaveguide antennas, bicone antennas, conformal antennas, and parabolicreflectors.
 21. The system of claim 1, wherein a position of at leastone of the plurality of antenna assemblies is configured to bedynamically adjusted along the length of the tension member while beingtowed by the aerial platform.
 22. The system of claim 1, wherein anorientation of at least one of the plurality of antenna assembliesrelative to the tension member is configured to be dynamically adjustedwhile being towed by the aerial platform.
 23. The system of claim 1,further comprising: a second tension member configured with a first endand a second end defining a length of the tension member, the first endconfigured to be secured to the aerial platform and the second endconfigured to extend from the aerial platform unsecured to the aerialplatform; and a second plurality of antenna assemblies secured to andspaced along the length of the second tension member, each of the secondplurality of antennas comprising at least one antenna configured for usewith electromagnetic radiation, wherein the antenna location system isconfigured to determine a relative location of each of the secondplurality of antennas, wherein the receiving system is configured toreceive information associated with the received coherentelectromagnetic radiation from each of the second plurality of antennas,and wherein the communication link is configured to communicativelyconnect each of the second plurality of antennas to the receivingsystem, such that information may be transmitted from each of the secondplurality of antennas to the receiving system.
 24. The system of claim23, wherein the first plurality of antennas associated with the firsttension member are configured to focus on a first area of the surfaceand the second plurality of antennas associated with the second tensionmember are configured to focus on a second area of the surface.
 25. Amethod for generating a three-dimensional mapping of a target surfaceusing synthetic aperture radar (SAR) data collected by a single pass ofan aerial platform, comprising: transmitting coherent electromagneticradiation to a target surface; securing a tension member from an aerialplatform, the tension member configured with a first end and a secondend defining a length of the tension member, the first end secured tothe aerial platform and the second end unsecured to the aerial platformand extending from the aerial platform at a different elevation than thefirst end; receiving reflections of the coherent electromagneticradiation from the target surface via each of a plurality of antennasassociated with antenna assemblies secured to and spaced along thelength of the tension member, each of the plurality of antennasconfigured to receive the coherent electromagnetic radiation;determining a relative location of each of the plurality of antennasusing an antenna location system; connecting each of the plurality ofantennas to a receiving system via a communication link; receiving, viathe receiving system, information associated with the received coherentelectromagnetic radiation from each of the plurality of antennas; andprocessing at least some of the received information associated with thecoherent electromagnetic radiation using a synthetic aperture radartechnique to generate a three-dimensional mapping of at least a portionof the target surface.
 26. The method of claim 25, wherein the syntheticaperture radar technique includes Doppler-beam sharpening.
 27. Themethod of claim 25, wherein the coherent electromagnetic radiationcomprises a series of coherent spatially-overlapping electromagneticpulses.
 28. The method of claim 25, wherein the tension member comprisesan electrically conductive material.
 29. The method of claim 28, whereinthe tension member comprises a plurality of insulating members spacedalong the length of the tension member, such that the tension member isdivided into a plurality of segments of electrically conductive materialseparated from one another via an insulating member, and wherein each ofthe plurality of segments is non-resonant at a predetermined frequencybandwidth.
 30. The method of claim 25, further comprising controlling alocation of the second end of the tension member relative to the aerialplatform using a control device.
 31. The method of claim 25, wherein theantenna location system is configured to utilize a global positioningsystem (GPS) to determine the relative location of each of the pluralityof antennas.
 32. The method of claim 25, wherein the antenna locationsystem is configured to utilize interferometry of a radio frequency (RF)signal to determine the relative location of each of the plurality ofantennas.
 33. The method of claim 25, wherein at least one of theplurality of antennas comprises an active antenna.
 34. The method ofclaim 25, wherein at least one of the plurality of antennas comprises aconformal antenna.
 35. The method of claim 25, wherein at least one ofthe plurality of antennas comprises an electronically steerable antenna,configured such that the physical antenna remains in a fixed form whilea beam angle of the physical antenna is electronically steerable. 36.The method of claim 25, further comprising a fixation device configuredto control an orientation of at least one of the plurality of antennas.37. The method of claim 25, wherein one of an orientation relative tothe tension member and a position along the length of the tensionmembers of one of the plurality of antennas is configured to bedynamically adjusted to improve reception of the coherentelectromagnetic radiation while being towed by the aerial platform. 38.The method of claim 25, wherein the communication link comprisesfree-space optical transmission network configured to allow each of theplurality of antennas to transmit information to the receiving system.39. The method of claim 25, wherein the communication link comprises anout-of-band wireless network configured to allow each of the pluralityof antennas to transmit information to the receiving system, theout-of-band wireless network utilizing frequencies out of apredetermined range of the coherent electromagnetic radiation.
 40. Themethod of claim 25, wherein the first end of the tension members isconfigured to be secured to an airplane.
 41. The method of claim 25,wherein the first end of the tension members is configured to be securedto a lighter-than-air-vehicle.
 42. The method of claim 25, wherein thefirst end of the tension members is configured to be secured to anorbiting satellite.